Rabbi Jacob Emden was born in Altona (near Hamburg) in the summer of 1697. His father Rabbi Tzevi Ashkenazi (known as the Chacham Tzevi) was then chief rabbi of the three sister communities of Altona, Hamburg and Wandsbeck (known in Jewish history as the 'Kehiloth AHU,' after the Hebrew initials of the communities).
Rabbi Jacob Emden's real name, as you see, was Ashkenazi, but he was called Emden after the city where he had served as rabbi. He is also known as YaBeTz, being the initials of the words Yaakov Ben Tzevi.
The young Jacob's first teacher was his own illustrious father, who was a famous Talmudist and rabbi in his time. From his father, Jacob inherited a fiery nature and violent opposition to the movement of the false 'Messiah' Sabbatai Tzevi. Although this movement 'had already long been proven as false and misleading, there were still secret followers of it. Like his father, he was determined to ferret them out and expose them at all costs.
Until the age of eighteen, Rabbi Jacob followed his father everywhere, when the latter took up position in Amsterdam and later in Lemberg. Then he left him to marry the daughter of a famous Talmudist Rabbi Mordecai ben Naftali Hakohen, who was the head of a great Yeshivah at Ungarish-Brod in Moravia. There he greatly enriched his knowledge of Torah by devoting most of his time to dilligent study. In his spare moments he also studied languages, grammar and philosophy.
After three years of intensive study, he left his father-in-law's house and Yeshivah at Brod and became a travelling salesman in jewelry. He did not want to become a paid rabbi if he could help it. Nevertheless, he never neglected to continue his studies even during his travels, and wherever he came he preached and reprimanded Jewish communities or leaders when he was not satisfied with their religious conduct.
In 1728 he accepted the call of the Jewish community at Emden to fill the vacant rabbinical post in that city. He held the post for four years, during which he was in continuous strife with all those who did not live up to his expectations. Finally he gave up the position, and returned to his native Altona in 1733. Here he spent the rest of his life, more than forty years of relentless fighting for his convictions, which brought him in conflict with the leading rabbis of his time.
On arrival in Altona. he was permitted to establish a synagogue of his own. He also started a printing shop, for which he had received the king's approval. In addition he conducted a thriving business in gems.
Soon Rabbi Jacob Emden printed a prayer book with commentaries which aroused a great deal of opposition because it contained radical changes. Rabbi Emden did not live at peace with the two leading rabbis of his community, Rabbi Moshe Chagis, head of the rich Portuguese community, and Rabbi Jezekiel Katzenelnbogen, chief rabbi of the triple communities, the position previously held by Rabbi Emden's father. He often criticised the latter's law decisions, disregarding his age and position, for when Rabbi Jacob Emden considered himself in the right he would respect no one who differed from him. For sixteen years he was a bitter opponent of the chief rabbi, until the latter's death in 1749, when Rabbi Jonathan Eybeschutz of Metz succeeded him.
Rabbi Jacob Emden suspected the new chief rabbi of being a secret follower of the Sabbatai Tzevi movement. He denounced him in public, and demanded that he be excommunicated.
The leaders of the community defended their Rabbi, who was well known as an unusually pious man and outstanding scholar. They declared that Rabbi Emden was a trouble maker and demanded that he leave the community. He refused to do so, until he was threatened with violence; then he fled to Hamburg and appealed to King Frederick of Denmark, to whom the province belonged. In June 1752 judgment was passed in favor of "Jacob Herschel" (Jacob the son of Hersch-Tzevi) as Rabbi Emden was called in the official documents. The Jewish community council was blamed for high-handed action in driving Rabbi Emden out, and the leaders were fined. Rabbi Emden was permitted to return to Altona, where he continued his attacks against Rabbi Jonathan Eybeschutz. Finally the king was convinced that Rabbi Emden was in the wrong and ordered him to stop his attack. The heated conflict was ended, but not before it had spread far and wide and kept Jewry in a state of excitement for a long time. It was generally agreed that although Rabbi Jacob Emden was prompted by good motives to defend Judaism against what he believed to be a grave danger, he was blinded by his zeal, and his fiery nature had the better of him.
There was, however, no difference of opinion as to Rabbi Jacob Emden's great scholarship. He 'was recognized as an authority on Jewish law and had great influence among government circles. Thus in 1772 he was called upon to help the Jewish community- of Mecklenburg Schwerin in its fight for the right to bury the dead soon after death, in accordance with the requirements of Jewish law, which regards a delay in burial as degrading to the dead.
In addition to his Siddur, which despite some opposition became an important reference book in connection with Jewish prayer, Rabbi Jacob Emden is the author of several other works. He wrote a diary "Megillath Sefer" which is of great historical interest, since it gives a clear picture of Jewish life in those days. He also wrote various pamphlets in connection with the many controversies in which he was involved. Such was his "Eiduth B'Yaakov" in which he presents his case against Rabbi Jonathan Eybeschutz. He wrote pamphlets in his fight against the Sabbatai Tzevi movement. Of greater importance are his commentaries on the Mishnah, called "Seder Olam," and the Siddur mentioned above, which are important contributions to Rabbinical literature, which gave him an important place among the leading Talmudists of his time.